All biological cells make decisions by adjusting concentrations of biochemical molecules. Because molecular levels in cells are discrete and often low, the probabilistic nature of individual chemical reactions significantly randomizes every cellular process. This non-genetic variability plays an important role in many different processes ranging from stem cell differentiation, to anti-tumor drug responses, and even DNA repair. The goal of our research is twofold. By analyzing models that describe molecular fluctuations in cells we want to understand the principles of how stochastic fluctuations are generated, transmitted, and eliminated within cellular processes. Secondly, we are developing mathematical tools to non-perturbatively identify biochemical reaction rates from single-cell fluctuation data.